A computer network is a collection of interconnected computing devices that exchange data and share resources. In a packet-based network, such as the Internet, the computing devices communicate data by dividing the data into small blocks called packets. The packets are individually routed across the network from a source device to a destination device. The destination device extracts the data from the packets and assembles the data into its original form. Dividing the data into packets enables the source device to resend only those individual packets that may be lost during transmission.
Certain devices within a network, referred to as routers, maintain routing information that describes available routes through the network. Each route defines a path between two locations on the network. Upon receiving an incoming data packet, the router examines header information within the packet to identify the destination for the packet. Based on the header information, the router accesses the routing information, selects an appropriate route for the packet and forwards the packet accordingly.
The network devices typically communicate packets in conformance with a communication protocol. Example protocols include the Internet Protocol (IP), Multiprotocol Label Switching (MPLS), Virtual Local Area Network (VLAN), Frame Relay, Asynchronous Transfer Mode (ATM), Layer 2 Tunneling Protocol (L2TP), and the Point-to-Point protocol (PPP).
Many conventional network protocols support class of service (CoS) information, which can be used in controlling traffic flow. For example, packets can be queued and forwarded based on the CoS information associated with each packet. In particular, prioritization schemes may be implemented in accordance with class of service information, and streams of packets may be assigned to different service levels. Higher priority packet streams receive higher forwarding priority. Example CoS information used by conventional protocols includes IP Type of Service (ToS), MPLS experimental (EXP) bits, VLAN user priority, and IPv6 traffic class. Typically, CoS information is encoded within the header information associated with each packet.
The various protocols often required different formats and techniques for supporting and communicating the CoS information. Consequently, network devices, such as routers, often employ complex mapping techniques to preserve CoS information when packets are forwarded from one forwarding domain to another, i.e., from one protocol to another. In effect, the network devices utilize the mapping techniques to reformat the CoS information carried by the packets based on the particular protocols being used.
Due to the large number of protocols, however, these mapping techniques quickly become very complex and cumbersome. For example, these mapping techniques typically require a unique mapping between every combination of protocols supported by the network device in order to ensure that CoS information can be correctly conveyed as packets are forwarded between the protocols. The number and complexity of these protocol mappings, therefore, increases substantially as the number of protocols supported by a network device increases.